This invention relates to a transition duct for a gas turbine engine, specifically to a novel and improved profile for a transition duct that results in lower operating stresses and extended component life.
In a typical can annular gas turbine engine, a plurality of combustors are arranged in a generally annular array about the engine. The combustors receive pressurized air from the engine's compressor, adds fuel to create a fuel/air mixture, and combusts that mixture to produce hot gases. The hot gases exiting the combustors are utilized to turn a turbine, which is coupled to a shaft that drives a generator for generating electricity.
The hot gases are transferred from the combustor to the turbine by a transition duct. Due to the position of the combustors relative to the turbine inlet, the transition duct must change cross-sectional shape from a generally cylindrical shape at the combustor exit to a generally rectangular arc-like shape at the turbine inlet. In addition, the transition duct undergoes a change in radial position, since the combustors are typically mounted outboard of the turbine. Extreme care must be taken with respect to the design of these ducts in order to avoid sharp geometric changes, otherwise regions of high stress and stress concentrations can occur. The combination of complex geometry changes as well as extreme mechanical and thermal loading seen by the transition duct can create a harsh operating environment that can lead to premature deterioration, requiring repair and replacement of the transition ducts. To withstand the hot temperatures from the combustor gases, transition ducts are typically air-cooled. A variety of methods are available to provide cooling such as through internal channels, impingement cooling, or effusion cooling.
Severe cracking, resulting in component failure and forcing engine shutdown, has been known to occur in transition ducts having extremely sharp geometry changes and internal air-cooled channels. In such an incident, the engine requires transition ducts replacement or repair prior to returning to operational status. The present invention seeks to overcome the shortfalls of these prior art designs.